In cosmetic technology there is today for light and wash resistant dyeing of human hair used practically only oxidation dyes, i.e. low molecular starting substances which are oxidized by means of H.sub.2 O.sub.2 to the desired colour. These low molecular starting substances readily penetrate into the hair, are there oxidized to large dye molecules and in this way fixed mechanically. This well-known method yields good colouring results, but nevertheless it is an important desire by the hair cosmetic industry to be able to have it replaced by methods which are simpler and kinder to the hair. A composition which satisfies modern requirements should not contain H.sub.2 O.sub.2 and should have a low pH value which today lies at a level as high as about 10.
An attempt in this direction has been to replace the oxidation dyes by dispersion dyes which are not water soluble but merely dispersible in water. These dyes, therefore, are not capable of penetrating appreciably into the hair even if the hair is strongly massaged in connection with the application of the dye. Where a mechanical fixing is possible a virtual dyeing process is required, which, however, starts only at an increased temperature, namely 40.degree. to 50.degree. C. Even if this temperature increase is moderate in itself and can easily be provided by usual heating means, for example by means of a heating hood, the actual dyeing thus takes place only during the heating of the hair. In this case a difficulty has been that one has not been able to apply sufficient amounts of the dyestuff in water-thin solution. This may be compensated for by making the dispersion more viscous, and attempts have also been made by means of thickening agents to obtain a composition which satisfies the condition of applying a sufficient amount of the dyestuff for the subsequent treatment at an increased temperature.
Up to now, however, one has not been successful in finding an acceptable thickening agent, since it must have suitable properties from a great many different aspects. By way of example it may be mentioned that thickening agents of the type of high molecular substances in most cases have a detrimental influence on the colouring in the heat treatment and/or produce deposits especially within the acid range. An exception from this is ammonium polyacrylate, which, however, on the other hand, is a pure glue and, therefore, affects the hair in an unfavourable way, in so far as it becomes rough and difficult to comb out even after vigorous rinsing.
Further, in hair dyeing preparations there are sometimes also used relatively highly concentrated surfactant solutions which in this concentration are viscous, for example nonyl phenols, or which become viscous after the addition of a slight percentage of common salt, for example shampoo, on the basis of ether sulfates. Nor are such viscous surfactant solutions suited for dispersion dyes. Even after heating, the dye particles in this environment adhere poorly to the hair apart from the fact that it is undesirable to let the skin come in contact with heated concentrated surfactant solution for a prolonged period of time.